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WILLIAM H. COLE 



fuse daylight, and with a bright light at one side all gave similar 

 results. A check experiment, in which the speed of revolution 

 was very low (from 1 to 40), showed the flies creeping about 

 indifferently; therefore it was concluded that mechanical and 

 light stimuli did not affect the response in these experiments. 

 One hundred trials with 40 different animals, under the various 

 conditions described above, showed that a speed of 60 revolu- 

 tions per minute was necessary to start them moving toward 

 the center. As the flies approached the center the speed had 

 to be gradually increased in order to keep them moving toward 

 the center. At a distance of 2 cm. from the center a speed of 

 approximately 210 revolutions per minute was necessary to ac- 

 complish this. At a distance of 25 cm. from the center any 

 speed greater than 100 revolutions per minute mechanically 

 prevented the flies from creeping toward the center. Table IV 

 gives the data for several trials taken at random from the series 



of 100. 



TABLE IV 



Showing the position of 14 flies in 8 trials after one minute of revolution at dif- 

 ferent speeds. 



These experiments demonstrate a very definite response and 

 prove that Drosophila reacts negatively to a centrifugal force 

 equal to or slightly greater than gravity, as well as to a gravi- 

 tational one, without regard to other stimuli. We may there- 

 fore consider gravity a kinetic stimulus as well as a directive one. 



